Thermally developable diazotype photoprinting material and production thereof



July 24., 1962 R. J. KLIMKOWSKI ET AL 3,046,128 THERMALLY DEVELOPABLE DIAZOTYPE PHOTOPRINTING MATERIAL AND PRODUCTION THEREOF Filed July 5, 1958 FIGI DIAZO LAYER $4 I g \I- PAPER 3 ALKALI GENERATING LAYER FIG. 2

v //7)"DIAZ0 LAYER It l PAPER 4 W fl RESINOUS PRECOAT 440/ A\ALKAL| GENERATING LAYER FIG. 3

5 L YPVAPOR BARRIER FILM 2 Z DIAZO LAYER PAPER 3 ALKALI GENERATING LAYER INVENTORS: ROBERT J. KLIMKOWSKI JOHN W KRUEGER ATT'YS atent Ciiice 3,@ib,l28 Patented July 24, 1962 3,946,128 THERMALLY DEVELUPABLE DIAZOTYPE PHOTO- PRINTTNG MATERIAL AND PRODUCTION THEREGF Robert .I. Kiimlrowshi, Chicago, Ill, and John W. Krue= ger, Cottage Gove, Wis., assignors to Eugene Dietzgen (10., Chicago, lib, a corporation of Delaware Filed July 3, 1958, Ser. No. 746,544 6 Claims. (Cl. 96-49) This invention relates to the production of diazotype photoprinting materials, and to new materials and methods. More particularly, the invention relates to improved thermally developable photoprinting materials characterized by good development and good storage or shelf life.

The diazotype reproduction processes are based on light-sensitive diazo compounds coated on a suitable base, and a colored, positive azo dye image is formed on the base from a positive master, Exposure to ultraviolet light under a translucent master or original, such as an engineering drawing, photographic positive, typed material or other design, will decompose the diazo compound where it has been struck by light, and retain the diazo compound where it has been protected from light by the opaque areas of the original. The print is then developed by reacting the retained diazo compound with a coupler, to form a highly colored azo dyestuff, in precise duplication of the original.

The diazotype reproduction processes are divided into two categories, the moist process and the dry process. The moist process is a one-component diazotype process in which the diazo is on the base while the coupler is applied to the coated surface in a developer solution. The dry process is a two-component process in which both the diazo and the coupler are on the base and in which development is achieved without wetting, such as through the use of moist ammonia vapors to induce the coupling reaction. The present invention is concerned with improvements in the dry process printing materials and in their manufacture and use.

Each of the above systems, though in commercial usage today, has serious disadvantages. The ammonia developed system is handicapped by the pungent, lachrymatory nature of the ammonia employed. Consequently the majority of ammonia-developed machines require special venting in order to eliminate this problem. In spite of these efforts, the solution to this problem is unsatisfactory. Ammonia must be handled in order to fill the machine, and venting does not allow a portable machine.

The second system (liquid developer), though eliminating the odor of ammonia and consequently the need for venting, is hampered by the fact that the developing solution must be mixed frequently and once mixed it is susceptible to oxidation. Furthermore, evaporation of Water from the developer induces crystallization and this combined with the aforementioned oxidation often leaves the developing section of a machine a brown sticky mass.

Attempts have been made in the past to obtain a diazotype printing paper developable by heat, but they have met with little or no success. These methods have included incorporation of the heat developing chemicals into or onto the sensitized side of the base employed. Inasmuch as the materials employed were capable of causing the sensitized coating to develop rapidly, the problem of storage life of the sensitized product was of such a magnitude that commercial production of the above was not feasible.

Whenever satisfactory storage life has been obtained,

2 it has been accomplished at the expense of development. Achievement of storage life has been possible only by such heavy stabilization that development would yield only a faint, weak reproduction in no Way comparable to that obtained from commercial diazotype papers.

It is therefore an object of the present invention to provide improved diazotype photoprinting materials and methods which overcome the disadvantages of the prior systems, and particularly, thermally developable photoprinting materials which have both good development and good storage characteristics.

A more particular object is to provide diazotype ma terials which are developed solely by the application of heat.

A further object is to provide a single photoprinting material for both exposure and development, with no need for other materials or solutions.

An additional object is to provide a completely dry photoprinting material and process which produce excellent permanent diazotype prints, not subject to darkening, discoloration or other undesirable changes thereafter, whether or not exposed to light, humidity or other conditions which are commonly encountered. Thus, the materials and photoprinting process of the invention are eminently suitable for office and shop use.

Another object is to provide photoprinting materials which are readily and economically prepared using commonly available and substantially stable materials.

A further object is to provide methods for producing photoprinting materials and for producing photoprints therefrom which do not require complex equipment or involved operations.

These and other objects, advantages, and functions of the invention will be apparent on reference to the specification and to the attached drawing illustrative of several preferred embodiments of the invention, described hereinafter.

The invention provides a thermally developable diazotype photoprinting material comprised of a vapor permeable base, a diazotype sensitizer on one side thereof, and on the reverse side, a compound which produces alkaline vapors when heated. The photoprinting process employing the material of the invention involves merely exposing the sensitized side of the material followed by application of heat to the reverse or alkali generating side for the production of alkaline vapors and develop ment of an image.

The invention provides an elfective barrier in the form of the base, such as paper, between the light-sensitive compound and the alkaline materials, to eliminate the possibility of their uniting prematurely with consequent undesirable precoupling. The photoprinting materials thus have the desired storage life for unexposed lightsensitized material. At the same time, the provision of a vapor permeable base coated on the reverse side with a material producing alkaline vapors results in excellent development.

The compounds which produce alkaline vapors when heated are preferably those which yield ammonia by decomposition or dissociation. The compounds include, for example, the preferred urea, guanidine, alkyl substituted ureas and the like. Other compounds which may be employed are the ammonium salts of weak acids such as ammonium acetate, ammonium carbonate, ammonium diglycolate, and ammonium oleate. Volatile organic bases may also be employed, for example, ethylene diamine, -N-(2-hydroxyethyl) 2-n1ethyl-1,2-propanediamine, and others. They do not liberate ammonia but themselves possess the required basicity.

It Will be apparent that the alkaline acting compounds must not have an appreciable alkaline vapor pressure at ambient temperatures, or precoupling will take place. It is therefore preferred that such vapor pressure be insubstantial at atmospheric temperatures and up to about 200 F. and preferably up to about 225 F. However, it is possible to employ compounds having a more substantial vapor pressure, by enclosing them in a resinous film or the like, as subsequently described. Satisfactory storage life can then be achieved with the interposition of the paper or other base. At the same time, it is preferred that substantial alkaline vapor pressure sufiicient for coupling be achieved below about 450 Otherwise, there is danger of decomposing the diazo compound. The upper temperature limit will vary with the thermal stability of the diazo compound.

In a preferred embodiment, the stability and shelf life may be enhanced by incorporating in the alkali generating layer, a compatible acidic stabilizing material, of a type and quantity which will not interfere with development. Weak preferably organic acids are most advantageously employed, such as tartaric, citric, diglycolic, oxalic, acetic, and malic acids. Those acids which decompose on heating are further preferred.

In a preferred practice of the invention, a light-sensitive diazo compound, an azo dye coupling component and adjuncts are applied to the side of the base opposite to the side containing the alkali generating material. The materials are applied to the respective sides in any order. The diazo compound, coupling component, and adjuncts are not critical factors in the practice of 'the invention.

Any diazo compound and coupler suitable for producing dry process diazotype materials may be used. Exemplary diazo compounds are the diazonium salts obtained by diazotization of the following amines:

p-Amino-N,N-dimethylaniline p-Amino-N,N-diethylaniline p-Amino-N-ethylaniline p-Amino-N-ethyl-N-fl-hydroxyethylaniline p-Amino-N-methyl-N-18-hydroxyethylaniline p-Amino-N,N-di-B-hydroxyethylaniline p-Arnino-m-ethoxy-N,N-diethylaniline p-Amino-N-ethyl-o-toluidine p-Amino-N-ethyl-m-toluidine p-Amino-N,N-diethyl-m-toluidine p-Amino-N-ethyl-N benzylaniline p-Amino-N-ethyl-N-B-hydroxyethyl-m-toluidine N-p-amino-phenylmorpholine p-Amino-diphenylamine 3-aminocarbazole and the like.

These diazonium salts are commonly employed as their stabilized double salts, e.g., their zinc chloride, cadmium chloride or stannic chloride double salts.

Exemplary suitable azo coupling components are the following: 2,3-dihydroxynapthalene 2,3-dihydroxynaphthalene-6-sulfonic acid Resorcinol Phloroglucinol Acetoacetanilide 7-hydroxy-1,2-naphthirnidazole l-phenyl-3-methyl-5-pyrazolone 2-naphthol-3,6-disulfonic acid, and the like It is also contemplated that in providing the azo dye coupling component on the sensitized surface of the base, a coupler capable of thermal transfer or vapor distillation may be provided on the unsensitized side with the alkaline material for transfer therewith to the sensitized side upon application of heat.

The diazo compounds and coupling components are applied to the base in conventional coating solutions and at standard rates of application. F or example, diazo compounds are conventionally applied to diazotype paper at the rate of 10 to 50 grams per 1000 square feet.

The various adjuncts usual in the manufacture of lightsensitive diazotype materials may be employed in the 4 sensitizing and coupling compositions, such as metal salts for intensification of the image, stabilizing agents, acids acting to retard precoupling, and others.

In a novel embodiment of the invention, a useful adjunct is a heat fugitive acidic stabilizer provided in the sensitizing solution. Thus, stannic chloride may be employed, and it will volatilize upon the application of heat. Citric acid also decomposes upon the application of heat. The efficiency of the photoprinting material may be improved thereby, it being possible to maintain high stability until such time as low stability and coupling of the diazo comuound is desired.

After exposure of the sensitized side of the material under a design to be reproduced, heat is applied to the reverse side for the production of alkaline vapors and development of an image of a design. The time and temperature of heating are selected for the system employed, to produce the requisite vaporization of alkaline material without undesirable decomposition of the diazo compound. The results are generally advantageous when the alkali generating materials are subjected to a relatively high temperature of about 300 F. to 400 F. for a short time, a period of about several seconds to about a minute. While the materials can be heated to a lower temperature for a longer period of time, the former procedure is preferred.

Upon heating, the ammonia-producing materials evolve ammonia which permeates the base throughout the same and completely and intimately contacts the sensitized layer, where the pH is raised sufliciently to produce the coupling reaction between the unexposed diazo compound and the coupling component, which produces the colored image.

Certain of the compounds or their decomposition products, such as urea, guanidine, and their derivatives, apparently undergo other reactions including possible recombination to urea and combination to other compounds. It appears that urea may be reconstituted on the sensitized side of the base, and it there further assists in the development.

When employing a volatile amine, it appears that a triazene may be formed intermediately by reaction with the diazo compound. The triazenes under the influence of heat decompose to the diazo compound which reacts with the coupler to produce the desired azo dye. In the event that an amine should form a stable triazene under the conditions of operation it would not be used, since the desired color reaction would not be obtained, although the triazene might be colored. O The new photoprinting material is preferably employed in combination with means for maintaining the alkaline vapors in contact with the sensitizer. Such means include provision during the heating and developing of apparatus for confining or restraining the vapors adjacent the sensitizer, e.g., a plate or the like, and/ or a vapor-restraining film on the sensitized side of the base. Such a film may be produced by incorporating a suitable resinous or equivalent material in the sensitizing solution, or by coating such a material over the sensitized layer, the resinous material being one of those more particularly described below in connection with the application of the alkaline material. In this manner, contact of the alkaline vapors with the sensitized layer is more complete and longer lasting, and the amount of alkaline material may be limited. However, it is also possible to effect development without restraining the vapors in such a manner, but a relatively high concentration of alkaline material may be required. The sensitized layer may also include finely divided silica, of the type subsequently described, to enhance the dye image and also assist in the penetration of the layer by the alkaline vapors.

It is preferred to incorporate the alkaline reacting material on the reverse side of the base with a film-forming resinous material or the like, which assists in preventing precoupling, and also prevents crystallization of certain of the materials. The film-forming ingredients may be either hydrophilic or hydrophobic, but hydrophobic materials are preferred. The hydrophobic natural and synthetic resins are preferred, such as rosin derivatives, and synthetic substantially water-insoluble film-forming synthetic resins.

The preferred resins are hydrophobic synthetic filmforming thermoplastic addition polymers of at least one mono-olefinic monomer having a polymerizable CH =C group, such as the polystyrene resins, the polyacrylic resins and the polyvinyl resins. The polystyrene resins include, for example, homoand copolymers of styrene, and ring and side chain-substituted styrene, substituted with halo, alkyl or aryl radicals. Thus, the polymers may be prepared from vinyl toluene, alpha and beta-chloro and bromo styrene or alpha and beta-methyl and ethyl styrene. The polyacrylic resins include the preferred polymers of acrylic esters, such as methyl and ethyl methacrylate, and methyl and ethyl acrylate. The polyvinyl resins include the vinyl esters such as vinyl acetate, the vinyl halides such as vinyl chloride, and the vinylidene halides. Especially preferred are the butadiene-styrene copolymers and polyvinyl acetate. The polyacrylates and polystyrene are also very useful.

The resins are preferably employed finely dispersed or emulsified in an aqueous coating composition for application to a base. In this form, they are generally believed to be in or near the colloidal particle size range, e.g., about microns or below. About 1 or 2. percent of an emulsifier may be employed to aid in forming a stable emulsion of the resin particles, in known manner. One or more resins may be provided in the coating composition and resulting layer. The compound producing alkaline vapors is then dissolved or dispersed in the aqueous resin composition to provide a solution thereof for application to the unsensitized side of the base.

It is further preferred that the foregoing developing composition also include finely divided silica, which apparently assists physically in the development. Colloidal silica is preferred, having a particle size of about 0.1 micron or below. The particle size may, however, range up to 10 microns. Aqueous finely divided silica dispersions may be prepared in known manner from a silica powder, and the dispersion may contain an agent to stabilize the colloidal suspension. Also, one of the various commercially available preparations of aqueous finely divided silica may be employed, including available materials ranging in particle size from 0.007 to 0.1 micron and greater.

The concentration of the alkaline reacting material in the composition applied to the base and the rate of application to the base should be sufficient to elevate the pH of the sensitized layer to that required for coupling, and an excess should be provided to compensate for losses and variations in distribution. For example, the applica tion of about 500 grams to 2000 grams, and at times to 3000 grams, of urea per 1000 square feet of diazotype paper is recommended. Other compounds producing alkaline vapors may be applied at rates corresponding thereto on the basis of the ammonia or other basic vapor evolved.

The proportion of the alkaline material in its composition should of course not be so small that the vapors would be hindered from evolving through the permeable base. Thus, it is generally preferred that the compound producing alkaline vapors be present in a proportion greater than about 2 parts per part by weight of film-forming material. Silica may be employed in a proportion up to about 5 parts per part by weight of resin, there preferably being employed about 0.1 part to 2.0 parts per part of resin.

An acidic material for enhancing the stability of the alkali generating material, as previously described, may be incorporated in a suitable proportion depending upon the nature of the acidic material and of the alkali generator. For example, about 8 to 2.0 grams of citric acid or about 10 to 40 grams of tartaric acid may be added to the alkaline composition of Example 1 which follows, the composition containing 125 grams of urea and 50 grams of guanidine carbonate. Citric acid alone has a yellowing tendency, and the preferred addition to the composition is a combination of 0.8 to 5 grams of citric acid with 10 to 15 grams of tartaric acid. The proportion of acidic material is thus generally minor relative to the alkali generating material so as not to interfere with development.

The several materials are deposited on the unsensitized side of the base from an aqueous solution or dispersion having a concentration of about 20% to by weight of dispersed and dissolved materials.

As is well known, it is necessary for water to be present in contact with the diazo compound and coupler for development to take place. The water requirement is not great, and frequently is supplied by the natural moisture content of the photoprinting material. Certain of the alkaline materials may evolve water vapor upon decomposition, such as ammonium carbonate.

To assist in the incorporation of water in the photoprinting material, a humectant may be included on either side of the base. A humectant or hygroscopic material in the sensitized layer will also assist in absorbing the alkaline vapors. Suitable humectants include such materials as zinc chloride and polyhydric alcohols, for example, glycerine, ethylene glycol and diethylene glycol. The presence of silica may also assist in retaining moisture in the printing materials.

The vapor permeable base is most advantageously paper, porous cloth or the like as employed in drafting and printmaking, or similar materials. It is necessary that the paper or other base provide a physical barrier between the respective light-sensitive and alkaline sides or layers of the photoprinting material prior to development, while being freely permeable to vapors. Standard commercial diazo process paper is suitable, preferably all sulfite paper stock. Paper having a rag content may also be used, although with increasing proportions of rag, it may be advisable to precoat the paper to increase the thickness of the barrier and/ or reduce penetrability. With the diazo process paper, the diazo sensitizer may penetrate to about one-thirtieth of the depth of the paper, and the reverse coating of alkaline material will not meet the diazo layer. The coating times and other conditions effecting penetration may be regulated to insure that the respective layers do not come in contact through the base.

Penetration may also be controlled by coating the base on either side with a vapor permeable precoat or layer, preferably of a resinous material and further preferably of a resin-silica layer of the type described above in connection with the application of the alkaline material. A precoat on the sensitized side also improves image density. A precoat solution may be applied which contains, for example, 5-35 of one of the resinous materials described above, and preferably also about 5-35 of the described finely divided silica. The resin to silica ratio is preferably within the range of about 4:1 to 124.

Several preferred embodiments of the invention are schematically illustrated in the attached drawings, each of which is an enlarged fragmentary cross section of coated paper. In FIGURE 1, a sheet of paper 1 is illustrated as provided with a dried coat or layer 2 of a dry process light-sensitive diazotype composition, which may or may not also contain a resin which provides a vapor-restraining film and silica, as described above. On the reverse side of the paper, an alkali generating layer 3 is provided which contains a compound producing alkaline vapors when heated. This layer also may or may not contain a resinous material and silica.

FIGURE 2 illustrates the sheet of paper 1 containing a dried precoat layer 4 of resin preferably also containing silica, on one side of the paper. The alkali generating layer 3 is provided over the precoat layer. The diazo layer 2 is provided on the reverse side of the paper in con- 7 tact therewith. Alternatively, the diazo layer and the alkaline layer may be transposed, so that the former is over the precoat and the latter is in contact with the reverse side of the paper.

FIGURE 3 illustrates the sheet of paper ll having the diazo layer 2 and the alkali generating layer 3 on opposite sides of the paper. A vapor barrier film 5 is also provided over the diazo layer, which may constitute a resinous material as previously described.

The following examples illustrate the materials and methods of the invention. It will be understood that the invention is not limited to the examples nor to the components, proportions, conditions and procedures set forth therein.

Example 1 A sensitizing solution for producing blueline diazotype prints has the following composition:

Water ml 100 Ethylene glycol ml 15 Citric acid g 0.75 Zinc chloride g 5.0 Thiourea g- 5.0

2,3-dihydroxynaphthalene-6-sodium sulfonate g 4.0

p-Diazo-N-ethyl-N hydroxy-ethylaniline zinc chloride salt g 1.4 Saponin -g 0.2

The sensitized solution is coated on a sheet of 100% sulfite diazo process paper, the excess being mechanically removed. The paper is then hot air-dried at 140 F. for about 2 minutes.

A coating composition containing a compound which produces alkaline vapors when heated is composed of the following ingredients:

Both the urea and the guanidine carbonate produce ammonia when heated. In place of the butadiene-styrene copolymer, the same quantity of a cationic polyvinyl acetate emulsion containing 50% solids, particle size 5-10 microns (Xyno X-99) may be used.

The combination of urea and guanidine carbonate is preferred, for excellence of development and considerations of solubilization and crystallization of the alkali generators.

To enhance the stability and shelf life, there may be added to the alkali generating layer 15 grams of tartaric acid, 10 grams of citric acid, or preferably, 10 grams of tartaric acid and 1.2 grams of citric acid.

The alkaline composition is coated on the unsensitized side of the paper, applying one coat by dipping and mechanically removing the excess, followed by drying at 140 F. for 2 minutes. The application deposits about 1250 grams of urea and 500 grams of guanidine carbonate per 1000 square feet of paper surface. The diazo compound is present on the reverse side in a quantity of about grams per 1000 square feet.

Alternatively, the respective coatings may be applied in the reverse order. The drying temperatures may be increased at shorter drying times. Thus, it is found that the sensitizing layer may be dried for several seconds with hot air, at 290 F., the alkali generating layer being present on the reverse side, without precoupling.

The photoprinting material is exposed to ultraviolet light under a design to be reproduced. The image is developed by applying heat to the alkaline side, such as by a hot metal plate, while confining the vapors evolved on the sensitized side by means of an additional metal plate 8 applied thereto. The temperature maintained on the alkaline side is about 350 F. for about 25 seconds. Intense blue reproductions are obtained in this manner.

Example 2 Instead of confining the vapors evolved by a plate or the like as described in Example 1, the sensitized surface of the paper may be sprayed with a resinous filmforming composition. A suitable composition is a poly acrylic lacquer containing 10% solids, 55% toluene and 35% ethyl alcohol.

Example 3 An alternative method of confining the alkaline vapors in contact with the diazo compound and coupler is to include a film forming resinous material such as polyvinyl acetate in the sensitizer composition of Example '1. For example, the sensitizer composition may additionally contain about 20 ml. of the Xyno X-99 emulsion.

Example 4 A sensitizing composition which may be substituted for that of Example 1 to produce blackline diazotype prints may have the following composition:

Water ml 100 Ethylene glycol ml 15 Citric acid g 0.7 Zinc chloride g 5.0 Thiourea g 6.0 Resorcinol g 0.2 77% thiourea-23% acetoacetanilide g 0.45 2,3-dihydroxynaphthalene-6-sodium sulfonate =g. 2.05 p-Diazo-N,N'diethylaniline Zinc chloride salt g 1.4 11% silica emulsion, 015-020, micron (Cab-osil) ml 25 Example 5 The following composition may be substituted for the sensitizer composition of Example 1, to produce rich sepia prints:

(Cab-o-sil) ml 10 The several photoprinting materials may also be made from up to 100% rag paper, depending upon the sizing, finish, and density of the sheet, with possible need for a precoat as described above.

11% silica emulsion Example 6 The alkaline composition of Example 1 may be substituted by the following composition:

Water ml 100 Urea g 50 Polyvinyl acetate emulsion, 55% solids, about 1 micron (Vinac HF) ml 25 Example 7 The alkaline composition of Example 1 may be substituted by the following composition:

Example 8 The alkaline composition of Example 1 may be substituted by the following composition:

The alkaline composition of Example 1 may be substituted by the following composition:

Ml. Water 100 30% colloidal silica emulsion (Ludox LS) 25 N-(2-hydroxyethyl) -2-methyl-1,2-propanediamine 50 Butadiene-styrene copolymer (Polyco 350W) 50 Example There may be added to the alkali generating compositions of Examples 6-9, 10 grams of tartaric acid and 1.2 grams of citric acid.

Example 11 A precoat or subcoat for coating paper may have the following composition:

Part Butadiene-styrene (40:60) copolymer latex, 48% solids, 0.2 micron particle size (Dow Latex 512R) 1 30% colloidal silica (Ludox LS) 1 Water 1 The pants here and subsequently are by weight.

This emulsion is coated on one side of the paper three times from a grooved roller with intermediate and final air drying at 140 F. for about 3 minutes.

The coated side of the paper is then coated five times from a grooved roller with intermediate air drying as before, with the following emulsion:

Part Butadiene-styrene latex (Dow Latex 512-R) 1 30% colloidal silica (Ludox LS) 1 Water 1 to which is added with stirring, a warm solution (120 F.) of the following composition:

The dried paper is sensitized on the reverse side with the following medium speed diazotype solution:

Water ml 400 Ethylene glycol ml 44 Citric acid g 12 Zinc chloride g 40 Thiourea g 20 2,3-dihydroxynaphthalene-6-sodium sulfonate g 12 p-Diazo-N,N-diethylaniline zinc chloride salt g 4.8 Saponin g 0.8 The paper is dried at 140 F. for 3 minutes.

The aforementioned applications place on the paper about 600 grams of butadiene-styrene and 350 grams of silica per 1000 square feet in the precoat. Application of the alkaline coat places about 1000 grams of urea, 250 grams of butadiene-styrene, and 150 grams of colloidal silica on the papers per 1000 square feet. About 30 grams of the diazo compound per 1000 square feet are placed on paper.

The diazotype photoprinting material so prepared is stable to at least 24 hours storage over a 50-50 glycerinewater solution at 140 F. Good development is exhibited when the back is pressed with a hot iron (about 400 'F.) for five seconds, with the sensitized face against a metal plate.

10 Example 12 Paper is coated three times on one side with intermediate and final drying at F., with an emulsion of the following composition:

Part Butadiene-styrene latex (Dow Latex 512 K) 1 30% colloidal silica (Ludox LS) 1 Water 1 The coated side is then coated five times with intermediate and final drying at 140 F., with the following developing composition:

Parts Butadiene-styrene latex (Dow Latex 512R) l 30% colloidal silica (Ludox LS) 1 Urea 5 Ethylene glycol 3 Water 6 The reverse side of the paper is sensitized as in Example 11. The paper exhibits a good shelf life, and good development when passed through a drum drier such as used to dry photographic rints, the development time being about 45 seconds With the drier at 350 F The invention thus provides a very satisfactory thermally developable diazotype photoprinting material, which is characterized both by good development and good storage life. The photoprinting materials are readily and economically prepared from available materials, and they may be transported and stored under normal conditions for sensitized paper. The photoprinting material is especially suited for ofiice and shop use without need for special procedures or complex equipment. Photoprints are produced simply by exposing the sensitized side of the material followed by application of heat to the reverse side for development. The invention overcomes the disadvantages of the prior dry diazotype processes, and especially, eliminates the ammonia problem. The invention also obviates the necessity for liquids and attendant disadvantages which accompany the moist diazotype process. Only a single photoprinting material is needed for both printing and developing.

The invention is hereby claimed as follows:

.1. Two-component diazotype photoprinting material adapted for exposure and thermal development which comprises a vapor permeable base selected from the group consisting of paper and cloth, an azo dye coupling component on said base, a light sensitive diazo compound capable of coupling with said component on the same side of said base as said coupling component, and on the reverse side a compound which produces alkaline vapors when heated to a temperature up to 400 F., said base providing a barrier between said diazo and coupling compounds and said vapor producing compound.

2. Photoprinting material as in claim 1 wherein said base is paper.

3. Photoprinting material as in claim 1 wherein said vapor producing compound produces ammonia when heated.

4. Photoprinting material as in claim 1 wherein said vapor producing compound is urea.

5. A diazotype photoprinting process which comprises providing a two-component diazotype photoprinting material adapted for exposure and thermal development including a vapor permeable base selected from the group consisting of paper and cloth, an azo dye coupling c0mponent on one side of said base, a light-sensitive diazo compound capable of coupling with said coupling component on the same side of said base as said coupling component, and on the reverse side a compound which produces alkaline vapors when heated to temperatures up to 400 F., said base providing a barrier between said diazo and coupling compounds and said vapor producing compound; exposing said first named side to light under the design to be reproduced; and applying heat to said reverse side to produce said alkaline vapors whereby an image of the design develops on the first named side of said base.

6. A process as in claim 5 wherein said vapor producing compound is urea.

References (Cited in the file of this patent UNITED STATES PATENTS 1,770,352 Murray July 8, 1930 FOREIGN PATENTS Great Britain Apr. 29, 1935 

5. A DIAZOTYPE PHOTOPRINTING PROCESS WHICH COMPRISES PROVIDING A TWO-COMPONENT DIAZOTYPE PHOTOPRINTING MATERIAL ADAPTED FOR EXPOSURE AND THERMAL DEVELOPMENT INCLUDING A VAPOR PERMEABLE BASE SELECTED FROM THE GROUP CONSISTING OF PAPER AND CLOTH, AN AZO DYE COUPLING COMPONENT ON ONE SIDE OF SAID BASE, A LIGHT-SENSITIVE DIAZO COMPOUND CAPABLE OF COUPLING WITH SAID COUPLING COMPONENT ON THE SAME SIDE OF SAID BASE AS SAID COUPLING COMPONENT, AND ON THE REVERSE SIDE A COMPOUND WHICH PRODUCES ALKALINE VAPORS WHEN HEATED TO TEMPERATURES UP TO 400*F., SAID BASE PROVIDING A BARRIER BETWEEN SAID DIAZO AND COUPLING COMPOUNDS AND SAID VAPOR PRODUCING COMPOUND; EXPOSING SAID FIRST NAMED SIDE TO LIGHT UNDER THE DESIGN TO BE REPRODUCED; AND APPLYING HEAT TO SAID REVERSE SIDE TO PRODUCE SAID ALKALINE VAPORS WHEREBY AN IMAGE OF THE DESIGN DEVELOPS ON THE FIRST NAMED SIDE OF SAID BASE. 